Methane has been in and out of the news recently. Titan and all that. However, when one looks up how methane comes to be here on earth, it always seems to mention that it is the result of the breakdown of some sort of cellular organisms. (aka Life). Um,so,er, ah, how does methane form in the great ‘out there’ of other planets, moons, and so on? And if it occurs ‘out there’ in such a manner, could it have instead occured here by similar means, without aforementioned cellular organisms breaking down?
Most methane currently present on the Earth is the result of the breakdown of other organics. We know this because it’s often found in conjunction with coal and oil, which we know to be formed similarly. But methane is actually a very simple molecule, and will be formed naturally whereever you have carbon and hydrogen available (which is pretty much everywhere, those being two of the more common elements in the Universe). In fact, the organic sludge on the early Earth which eventually developed into life was itself largely formed from methane in the atmosphere.
Too add to what Chronos said, a methane molecule is a carbon atom with four hydrogen atoms stuck on to it. Pretty simple, and this will form naturally if you have carbon near hydrogen, as long as there isn’t oxygen to screw things up. Other petroleum products have much more complex molecules (still mostly carbon and hydrogen, but in longer chains). These aren’t likely to form by themselves without life.
Would this summary be correct?
-Methane is there to start with.
-Life comes and eats the Methane, leaving a more nitrogen atmosphere.
-Plants produce oxygen.
At this point, most of the methane is caught in a cycle, being both taken up and liberated by organisms and being oxydized out of the atmosphere.
(I know that there is a lot of carbon dioxide in the atmosphere, but I’m not sure whether to put it before or after the plants.)
So the exciting thing about methane is that it matches what the earth had at the beginning, since the earth then went on to produce life.
Imagine an upside-down bell-shaped curve representing chemical energy on the y-axis; lower energy means the compound is more stable. Elemental carbon is at the middle. Carbon dioxide is at one end, representing a highly oxidized compound, one from which electrons have been removed from the carbon. Methane is at the other, representing a highly reduced compound, one to which electrons have been added to the carbon. In other words, methane is the most stable compound that can be made by adding electrons to carbon, and carbon dioxide is the most stable compound that can be made by removing electrons from carbon. Therefore, a planet is likely to have a lot of either methane or carbon dioxide, depending on the conditions of its atmosphere. If it has a strongly reducing atmosphere, without much oxygen (and with other reducing compounds in it), you’ll expect to find most of its carbon in the form of methane. If it has an oxidizing atmosphere, you’ll find a lot of carbon dioxide. (Earth doesn’t have as much carbon dioxide as it should because it has liquid water; much of the carbon dioxide dissolved in the oceans and was deposited as limestone sediments.)
On Earth, of course, most of the atmospheric methane is from biological sources – bacteria that produce methane, primarily as a waste product from metabolizing sugars or other organic compounds. On Titan, though, the methane is probably present because its atmospheric conditions favor the production of methane from the carbon present in its atmosphere. In other words, if you left a huge chunk of charcoal on the Earth’s surface for a long time, eventually you’d get carbon dioxide; on Titan you’d get methane. But the presence of methane on Titan doesn’t mean there’s life there; in all likelihood, it was not formed biologically, as methane is on Earth.
That doesn’t mean life is impossible; it’s theoretically possible that there might be some single-celled organisms that produce CO[sub]2[/sub] from the methane there. If we found traces of carbon dioxide in Titan’s atmosphere, that might be a sign that there was life there.